Conventionally, (1) a high pressure vapor sterilization method or (2) an ethylene oxide sterilization method has been used in order to sterilize instruments used for surgical procedures or remedial treatments in medical institutions such as hospitals and the like.
In these high pressure vapor sterilization method and ethylene oxide sterilization method, it is extremely important (1) to determine whether instruments and other products to be sterilized have experienced a sterilization treatment process or (2) to detect whether sterilizing conditions applied to instruments are appropriate.
In a method of the determination method or the detecting method, a chemical indicator for sterilization whose color tone is changed by sterilization has been used, however, as the indicator for sterilization, a dedicated indicator for each sterilization method should be used.
However, the high pressure vapor sterilization method which has been conventionally used can be applied to only instruments which are resistant to high temperature and high pressure. On the other hand, the ethylene oxide gas sterilization method can be performed under relatively low temperature (40 to 60° C.) so that this method is often employed for sterilization of an endoscope, a plastic instrument which is heat-sensitive or the like. However, since strongly poisonous ethylene oxide is adsorbed onto the instruments after sterilization so as to tend to remain, this method has the disadvantage of requiring removal of the ethylene oxide which has adhered to the instruments after sterilization.
Recently, as a sterilization method which can replace the high pressure vapor sterilization method or the ethylene oxide sterilization method, a plasma sterilization method utilizing bactericidal ability of low temperature gas plasma with an oxidative gas such as hydrogen peroxide and the like or other gases has been used.
According to the sterilization process of the plasma sterilization method using “STERRAD 100” (trademark) which is one of presently commercially available typical hydrogen peroxide low temperature plasma sterilizers developed by Johnson & Johnson Medical (the United States), instruments to be sterilized are loaded into the inside of the sterilizer, and the inside of the sterilizer is highly evacuated, and then, a fixed amount of a hydrogen peroxide solution is injected and vaporized, the step of diffusing the vaporized hydrogen peroxide gas thoroughly over the inside of the strilizer (diffusion step, about 50 min) and the subsequent step of generating a plasma from the hydrogen peroxide gas by applying a high frequency voltage (plasma generation step, about 15 min) are provided.
In this plasma generation step, a plasma is generated from the hydrogen peroxide gas so as to contain many free radicals such as highly reactive .O radicals, .OH radicals or .OOH radicals, thereby providing an noticeable improvement in an sterilization effect compared to sterilization performed merely in hydrogen peroxide (for example, U.S. Pat. No. 4,169,123), and as a result thereof, sterilization can be performed at a temperature as low as about 45° C., and beside, can be realized for a short'time as mentioned above.
After the plasma generation step, when stopping applying high frequency energy, the plasma state ceases instantaneously so that highly reactive free radicals and the like recombine to form oxygen and water thereby allowing hazardous substances not to remain.
The applicant of the present application has already proposed a chemical indicator used for such a new low temperature gas plasma sterilization method using hydrogen peroxide (refer to the specification of Japanese Patent Application No. H 9-365688 or Japanese Patent Application Laid-Open No. H 11-178904 or the like).
The technical content of the above mentioned application by the applicant of the present application is based on the principle that “an indicator including a basic pigment such as triphenylmethanes and the like and a certain color change assistant is discolored colorless by oxidizing power of a plasma formed from hydrogen peroxide or a hydrogen peroxide vapor.”
It is an object of the present invention to provide an indicator wherein, contrary to the indicator of the above mentioned application, colorless pigments as used in pressure-sensitive copying papers or thermosensitive recording papers are used so that the indicator is clearly colored by the action of a plasma from hydrogen peroxide or a hydrogen peroxide vapor and has good stability in storage.